Synergy between stimulator cells in the induction of the anti-Mlsa response.

We have identified two types of clones responsive to Mls determinants. One type responded vigorously to purified B cells from mice bearing Mlsa-stimulatory determinants. The other type, including clone Ly1-N5, responded vigorously to unfractionated spleen cells, but failed to respond to B cells alone or to spleen-adherent cells (SAC) alone from the Mlsa-bearing mice. Synergy between two stimulator cell types, B cells and SAC, was required to induce the Mls response of clone Ly1-N5. The failure of clone Ly1-N5 to respond to Mlsa-bearing B cells was reversed by the addition of SAC taken from mice bearing the Mlsa allele or the non-stimulatory Mlsb allele. B cells were required to provide the Mlsa determinant. The Mls response of clone Ly1-N5 is restricted by class II determinants shared by the H-2b, H-2d and H-2k haplotypes, but not the H-2q haplotype. The optimal response of the clone was obtained by using B cells bearing both Mlsa and the permissive H-2 alloantigen. However, complementation was also observed between B cells bearing Mlsa and the non-permissive Iaq and SAC bearing the nonstimulatory Mlsb, but a permissive Ia epitope, resulting in activation of the clone. Clone Ly1-N5 responds to Mlsa-bearing B cells only in the presence of SAC.(ABSTRACT TRUNCATED AT 250 WORDS)